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Randomized controlled trial

A randomized controlled trial (RCT) is a type of statistical experiment designed to evaluate the efficacy or safety of an intervention by minimising bias through the random allocation of participants to one or more comparison groups.[1]

In an RCT, at least one group receives the intervention under study, such as a drug, surgical procedure, medical device or diet, while the other groups receive an alternative treatment, a placebo, or standard care.[2] Random assignment reduces selection bias and allocation bias, and it balances both known and unknown prognostic factors between the groups.[3]

Allocation concealment is the procedure for protecting the randomisation process so that the treatment to be allocated is not known before the patient is entered into the study.[4] Standard methods include sequentially numbered, opaque, sealed envelopes, sequentially numbered containers, pharmacy-controlled randomisation and central randomisation.[5]

RCTs can be classed as explanatory or pragmatic.[6] Explanatory RCTs test efficacy in a research setting with highly selected participants and under highly controlled conditions, whereas pragmatic RCTs test effectiveness in everyday practice with relatively unselected participants and under flexible conditions.[6] RCTs can also be classed as superiority, noninferiority or equivalence trials.[7] Most RCTs are superiority trials, in which one intervention is hypothesised to be superior to another in a statistically significant way.[7]

Why it matters to investors

A randomized controlled trial can provide compelling evidence that the study treatment causes an effect on human health.[8] RCTs are widely considered one of the highest-quality sources of evidence in evidence-based medicine, although they have also been criticised for failing to reduce bias in some cases.[9]

Related: Double-blind study, Phase 3 trial, Phase 2 trial

Sources

  1. Chalmers TC, Smith H, Blackburn B, et al. (May 1981). "A method for assessing the quality of a randomized control trial". Controlled Clinical Trials . 2 (1): 31– 49. doi : 10.1016/0197-2456(81)90056-8 . PMID 7261638 . doi.org (via Wikipedia: Randomized controlled trial)
  2. "What Are Clinical Trials and Studies?" . National Institute on Aging, US National Institutes of Health. 22 March 2023. Archived from the original on November 14, 2023 . Retrieved 9 March 2024 . web.archive.org; "What Are the Different Types of Clinical Research?" . US Food and Drug Administration. 4 January 2018. Archived from the original on June 12, 2019 . Retrieved 9 March 2024 . web.archive.org (via Wikipedia: Randomized controlled trial)
  3. Moher D, Hopewell S, Schulz KF, et al. (March 2010). "CONSORT 2010 explanation and elaboration: updated guidelines for reporting parallel group randomised trials" . BMJ . 340 : c869. doi : 10.1136/bmj.c869 . PMC 2844943 . PMID 20332511 . ncbi.nlm.nih.gov (via Wikipedia: Randomized controlled trial)
  4. Forder PM, Gebski VJ, Keech AC (January 2005). "Allocation concealment and blinding: when ignorance is bliss". The Medical Journal of Australia . 182 (2): 87– 89. doi : 10.5694/j.1326-5377.2005.tb06584.x . PMID 15651970 . S2CID 202149 . doi.org (via Wikipedia: Randomized controlled trial)
  5. Schulz KF, Grimes DA (February 2002). "Allocation concealment in randomised trials: defending against deciphering" (PDF) . Lancet . 359 (9306): 614– 618. doi : 10.1016/S0140-6736(02)07750-4 . PMID 11867132 . S2CID 12902486 . Archived from the original (PDF) on September 11, 2012. wayback.archive-it.org (via Wikipedia: Randomized controlled trial)
  6. Zwarenstein M, Treweek S, Gagnier JJ, et al. (November 2008). "Improving the reporting of pragmatic trials: an extension of the CONSORT statement" . BMJ . 337 a2390. doi : 10.1136/bmj.a2390 . PMC 3266844 . PMID 19001484 . ncbi.nlm.nih.gov (via Wikipedia: Randomized controlled trial)
  7. Piaggio G, Elbourne DR, Altman DG, et al. (March 2006). "Reporting of noninferiority and equivalence randomized trials: an extension of the CONSORT statement" (PDF) . JAMA . 295 (10): 1152– 1160. doi : 10.1001/jama.295.10.1152 . PMID 16522836 . researchonline.lshtm.ac.uk (via Wikipedia: Randomized controlled trial)
  8. Hannan EL (June 2008). "Randomized clinical trials and observational studies: guidelines for assessing respective strengths and limitations" . JACC. Cardiovascular Interventions . 1 (3): 211– 217. doi : 10.1016/j.jcin.2008.01.008 . PMID 19463302 . doi.org (via Wikipedia: Randomized controlled trial)
  9. Krauss A (June 2018). "Why all randomised controlled trials produce biased results" . Annals of Medicine . 50 (4): 312– 322. doi : 10.1080/07853890.2018.1453233 . PMID 29616838 . doi.org (via Wikipedia: Randomized controlled trial)

Checked 8 October 2026. How we check sources